The surface area is the area of all the faces of the solid.
So, it is composed by the two triangles (front and rear) and the two lateral rectangles.
The triangles have base 12 and height 8 (both given), so their area is

The rectangles have base 14 and height 10 (both given), so their area is

Finally, there's a base rectangle with dimensions 14 and 12, which has area

The surface area is made of two lateral rectangles, one base rectangle and two triangles, so it is
